R90 is about 10 USD right?
If so, that's probably too cheap. See the thing is, it's very easy to get caught up listening to audiobook after audiobook without really taking the time to reflect upon them. Your mind needs quiet time, devoid of sensory input to assimilate that information. Brian Tracy's very strong on this and it took me a long time to understand its importance.
Similar how we tend to fall in love in the breaks between dating someone, you get the most from audiobooks after listening to them, not during. I purposely restrain myself to listening audiobooks about 50% of my idle-brain time while cleaning, driving or walking the dog. It's when I'm not listening to them have I had my biggest breakthroughs in my work or being.
The cost of the audiobook ensures you give it a chance, rather than just moving onto a new one that sounds more exciting. I think it was Jim Rohn who, when younger, was annoyed that he had to pay expensive tuition fees up front, but then realised later the brilliance of such a system because it made him stick to it. If it were free or trivially cheap, it'd be too easy to drop out.
And of course, as Confuscius said, "Knowledge without practice is useless, practice without knowledge is dangerous." Audiobooks can be addictive because it's much easier to listen than to do something, and they're easy to justify because you're actually working on your self. Don't let the motivation that audiobooks give lure you into a false sense of security that you're actually doing something, or even developing.
All that said, YouTube has heaps of seminars that you can listen to on the run if you have a decent mobile broadband connection or ability to dump them locally. Also remember that if you do run your own business, their cost will be a tax deduction.
Overall the cost of audiobooks is a pittance for what they offer in the long run. Borrow if you have to. They train you for business that you must sometimes invest up front rather than avoiding expenses at all cost.